A plastisol in which a fine particle of polymer is dispersed in a plasticizer as a medium has been utilized in a variety of industrial applications, but a vinyl-chloride plastisol (hereinafter, referred to as “PVC sol”) using a polyvinyl chloride is used in most of these applications. Owing to their good processability and physical properties, PVC sols have been used in a wide variety of applications such as wallpapers, undercoats for an automobile, body sealers for an automobile, carpet backing materials, floor materials, paints and toys, and thus industrially carries significant value.
Besides many properties such as strength after curing by heating, elongation, rubber elasticity, flexibility, low-temperature properties and damping, a PVC sol exhibits good workability in a sol state before curing by heating and good processability.
“Good workability” as used herein means that a relatively smaller amount of a plasticizer may be combined to a fine particle of polymer and that a resulting sol has a lower viscosity so that it may be easily introduced in a variety of processing lines. In other words, to a certain amount of a plasticizer, a larger amount of an inorganic filler may be added. Such a plastisol which can be formed with a small amount of a plasticizer permits freedom in compounding, may be easily introduced in a processing line and can be widely applied regardless to an application.
The fact that a small amount of a plasticizer may be combined with a fine particle of polymer considerably contributes for improving not only workability but also physical properties of a molding. For example, a smaller amount of a plasticizer in a molding may prevent bleed-out of the plasticizer with time and may improve strength or an elastic modulus of a molding.
However, a PVC sol or an article prepared therefrom generates hydrogen chloride gas during incineration, which is believed to cause problems in relation to the environment and an incinerator such as considerable damage to the incinerator and acid rain due to hydrogen chloride gas discharged to the air. More recently, the gas has been believed to be one of causes generating extremely poisonous substances such as dioxins. There has been, therefore, needs for developing an alternative material because of strong concern about adverse affect to a human body or the global environment.
Such environmental problems are associated with not only a PVC sol but also a plastisol using a halogen-containing polymer in general. It has been, therefore, desired to develop a plastisol using a polymer without halogen atoms, i.e., a non-halogenated plastisol. As one candidate, an acrylic plastisol using an acrylic polymer (generally called an “acrylic sol”) has been proposed.
There have been proposed procedures for reducing the content of chlorine atoms in order to solve the above problems in a PVC sol. For example, JP-As 60-258241, 61-185518 and 61-207418 have proposed an attempt that a complex is formed from vinyl chloride and another polymer material such as an acrylic polymer to provide a plastisol with a reduced chlorine content.
Although the halogen content is reduced in such a plastisol, it still contains halogen atoms. Thus, the problem of generation of hydrogen chloride gas or dioxins during incineration has not been essentially solved.
JP-As 7-233299 and 8-295850 have proposed a plastisol using a particulate acrylic polymer, i.e, an acrylic sol as a non-halogenated plastisol with no halogen atoms.
Generally an acrylic sol has a quite similar appearance to a PVC sol, but the former has considerably different properties of a fine particle of polymer and therefore quite different workability or processability. For example, even when an acrylic sol and a PVC sol are prepared as a fine particle of polymer having the same particle size and size distribution, they exhibits considerably different viscosity, thixotropic properties and leveling properties. Therefore, in developing an acrylic sol or an article therefrom, an acrylic sol with desired properties cannot be obtained when employing known technique and information for a PVC sol as such.
These publications have disclosed an acrylic sol just for proposing a non-halogenated plastisol as an alternative material to a PVC sol. Its workability is significantly lower than that for a PVC sol.
For example, in the acrylic sol described in the publications, the lower limit of a plasticizer required for solation is considerably higher and a resulting plastisol has a higher viscosity so that it cannot be easily introduced in an existing processing line, i.e, reduced workability; a molding cannot be quickly formed in a short period; and a resulting article exhibits lower strength, i.e., reduced processability. A relatively higher amount of a plasticizer may leads to its bleed-out with time from the resulting article. Furthermore, a sol viscosity increases at a higher rate so that the sol has a shorter shelf life and a shorter working life.
In terms of workability in spray coating using, for example, an airless spray, an acrylic sol proposed in the previous publications cannot provide viscosity properties required for spray coating. In particular, it cannot be used for an application involving an airless-spray coating such as an undercoat or body sealer for an automobile.
For example, JP-A 8-3411 has described that an acrylic sol disclosed therein can provide a low-viscosity sol whereby uneven coating may be prevented. It, however, has a too high viscosity to be used in an airless spray. When adding a large amount of a plasticizer for reducing a viscosity, a coated sol may generate sagging so that an adequate film thickness or coating pattern cannot be maintained. When a reduced amount of a plasticizer is added to increase a viscosity for avoiding sagging, sagging can be prevented while airless-spray coating itself cannot be conducted due to an excessively higher viscosity. Thus, the prior art has not provided an acrylic sol having viscosity properties required for airless-spray coating.
There have been no descriptions of a non-halogenated plastisol without halogen atoms which generate toxic materials such as hydrogen chloride and dioxins during incineration and exhibiting good workability and processability.